Much like the Git and GitHub relationship, we have the Composer and Packagist relationship. While Composer itself is the actual tool, Packagist is the default repository service that provides packages for Composer. Service is easy enough to let us find packages we would like to use for our project. Without getting into the internals, it is suffice to say that the composer tool understands where to get the code for each of the packages hosted on Packagist.
The Packagist repository service is hosted at https://packagist.org:
The popularity of Composer over time can be easily observed through the https://packagist.org/statistics page, which shows the rapidly increasing number of packages in the Packagist repository over the course of few years:
